Unsolicited message rejecting communications processor
The spam blocker monitors the SMTP/TCP/IP conversation between a sending message transfer agent MTA—0 and a receiving message transfer agent MTA—1; catches MTA—0's IP address IP—0, MTA—0's declared domain D—0, sender_address A—0; and recipient A—1; and uses this source and content based information to test for unsolicited messages. It interrupts the conversation when MTA—0 sends a command specifying the recipient (an “RCPT” command) and uses the various test results to decide if the message is suspected of being unsolicited. If the message is suspected of being unsolicited then it logs the rejected message, sends an error reply to MTA—0 which forces MTA—0 to terminate the connection with MTA—1 before the body of the message is transmitted; else it logs the allowed message, releases the intercepted RCPT command which allows the conversation between MTA—0 and MTA—1 to proceed.
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This application is a continuation of application Ser. No. 10/238,812 entitled “An Unsolicited Message Rejecting Communications Processor,” filed on Sep. 9, 2002, which is incorporated herein by reference in its entirety as if set forth in full.
This invention is related to co-pending applications, application Ser. No. 10/238,076 entitled “An Unsolicited Message Diverting Communications,” filed on Sep. 9, 2002 by the same inventors and application Ser. No. 10/238,216 entitled “An Unsolicited Message, Intercepting Communications Processor,” filed on Sep. 9, 2002 by the same inventors.
BACKGROUND OF THE INVENTION1. Field of the Inventions
This invention blocks unsolicited e-mail messages, commonly known as SPAM, from a client's e-mail server; while reducing Internet traffic, local LAN traffic, and local storage.
2. Background Information
E-mail has become an important means of communications. Unfortunately, unsolicited e-mail messages, commonly referred to as SPAM, is cluttering this communications channel. This unsolicited e-mail wastes Internet bandwidth, local area network bandwidth, and storage. This translates into lost productivity, increased computing and increased communication costs. Some of this unsolicited e-mail is also offensive and inappropriate for non-adult audiences.
The spammer collects a list of e-mail address, append these addresses to their message, and queues these messages on their e-mail server (message transfer agent), 2, in
There are four basic approaches to trying to detect junk e-mail messages. One approach used a community set of rules to determine whether or not a message is spam. This approach is used in Razor, an open source Linux solution, and by companies such as CloudMark (based on Razor) and SpamNet. The problem is getting a community of users to agree on a common set of rules.
A second approach uses a set of rule base filters which are periodically updated by the provider and downloaded by the client to determine whether or not a message is spam. The problem is that the set of rules have to be updated and downloaded periodically.
A third approach uses a set of permissions to determine whether or not a message is spam. The problem is that it is impossible for somebody not on a user's permission list to send a message to the user.
A fourth approach uses a “whitelist” and a “blacklist” to determine whether or not a message is spam. The problem is that the spammers are constantly changing their return address and declared domain names.
There are three basic ways of implementing these approaches. One implementation approach is in the Message transfer agent. This approach adds some rules to the MTA. The problem is that the MTA program is complicated and inflexible. This limits the kind of rules that can be implemented.
A second implementation approach involves placing the filters between the e-mail client and the Message Transfer Agent. The problem is that some of the information which can be used to help determine whether or not a message is spam is lost or buried.
A third implementation approach involves adding some filters to the e-mail client, Mail User Agent (MUA). The problem is that the e-mail client add-in interface is not an open standard. This causes compatibility problems.
One problem with these approaches is that they are “reactive.” The spam has already been received by the server and relayed via a local area network to client's computer. The spam message has already consumed the server's Internet bandwidth, local area network bandwidth, and client storage.
Another problem with many of these approaches is that they are based on the from-address, the subject line, or content of the message; all of which can be easily forged or changed.
OBJECTS AND ADVANTAGESAccordingly, the several objects and advantages of my invention are:
- a) to provide a procedure which eliminates unsolicited messages from a client's e-mail mailbox;
- b) to provide a procedure which reduces the amount of the client's Internet bandwidth consumed by unsolicited messages;
- c) to provide a procedure which reduces the amount of communications bandwidth between a client's message transfer agent and mail user agent consumed by unsolicited messages;
- d) to provide a procedure which reduces the amount of storage consumed by unsolicited messages;
- e) to provide a procedure which uses information which can not be forged to improve the ability to block unsolicited messages;
- f) to provide a procedure which avoids the need for users to install software on their individual system;
- g) to provide a procedure which eliminates any need to change the client's current message transfer agent;
- h) to provide a procedure which logs the messages which have been allowed;
- i) to provide a procedure which logs the messages which have been rejected;
- j) to provide a procedure which allows users to select the ability to not block unsolicited messages;
- k) to provide a procedure which allows users to select the ability to block unsolicited messages;
- l) to provide a procedure which gives feedback to the sender of a blocked message;
- m) to provide a procedure for blocking unsolicited messages which is failsafe; and
- n) to provide a procedure for blocking unsolicited messages which is scalable.
Further objects and advantages of our invention will become apparent from a consideration of the drawings and ensuing description.
SUMMARY OF THE INVENTIONThe spam blocker monitors the SMTP/TCP/IP conversation between a sending message transfer agent MTA_0 and a receiving message transfer agent MTA_1 and catches the IP address IP_0 of MTA_0; the declared domain D_0 of MTA_0; the from-address A_0; and the to-address A_1.
The spam blocker uses the captured information to run various source and content based tests. IP_0 is used to query a DNS server for the real domain name DD_0. DD_0 is tested to see if it is “no name.” IP_0 is tested to see if it is in a open relay database. IP_0 is tested to see if it is not in a allow_address database. IP_0 is tested to see if it is in a prevent_address database. DD_0 and MTA_1's domain name D_1 are tested to see if they match. D_0 is tested to see if it does not match DD_0 and if D_0 is in the suspect_domain database. A_0 is tested to see if any portion of it is in the bad_from database. The domain of A_0 is tested to see if does not match DD_0 and if it is in the suspect_domain database. A_1 is tested to see if it is in the no_filter database. A_1 is tested to see if it is not in the yes_filter database. A_1 is tested to see if it matches A_0.
The spam blocker interrupts the conversation between MTA_0 and MTA_1 when MTA_0 sends a RCPT command and uses the results of the various tests to decide if the message is suspected of being unsolicited.
If the message is suspected of being unsolicited then the spam blocker logs the rejected message in a rejected_connection database and sends an permanent negative completion reply to MTA_0 which forces MTA_0 to terminate the connection with MTA_1 before the body of the message is transmitted.
If the message is not suspected of being unsolicited then the spam blocker logs the allowed message in the allowed_connection database, releases the intercepted RCPT command, and allows the conversation between MTA_0 and MTA_1 to proceed.
In overview, a user, 8, in
The present invention, a spam blocker, 18, in
As mentioned previously, the operations of spam blocker is tightly coupled with the SMTP protocol. The SMTP protocol consists of a set of commands and a set of replies. The set of commands, HELO, MAIL, RCPT, DATA, RSET, SEND, SOML, SAML, VRFY, EXPN, HELP, NOOP, QUIT, and TURN is shown in
As an example, the time line of a normal mail transfer is shown in
MTA_0 sends a message to MTA_1 requesting to establish a connection. MTA_1 then responds with a 220 rely which includes it's domain name D_1. MTA_0 then sends a HELO command with it's declared domain name D_0. MTA_1 then responds with a 250 reply to acknowledge the successful completion of the HELO command. MTA_0 then sends a MAIL command with a message from-address A_0. MTA_1 then sends a 250 to acknowledge the successful completion of the MAIL command. MTA_0 then sends a RCPT command with a to-address A_1. MTA_1 then sends a 250 reply to acknowledge successful completion of the RCPT command. MTA_0 then sends a DATA command. MTA_1 then sends a 354 reply to acknowledge its ability to receive the data. MTA_0 then sends the data, the body of the message. MTA_0 then sends a .\r\n to indicate the end of the data. MTA_1 then sends a 250 to acknowledge successful transfer of the data. MTA_0 then sends a QUIT command. MTA_1 then sends a 221 to acknowledge the QUIT command and closes its end of the TCP connection. Upon receipt of the 221 reply MTA_0 closes its end of the TCP connection.
As mentioned previously, the present invention, a spam blocker, 18, in
Time lines illustrating the interactions between MTA_0, spam blocker, and MTA_1 are shown in
If the message is not suspected of being spam then the interactions between MTA_0, spam blocker, and MTA_1 proceed as shown in
If the message is suspected of being spam then the interactions between MTA_0, spam blocker, and MTA_1 proceed as shown in
It should be noted that the spam blocker terminates the connection with MTA_0 before the body of the message is transferred. This saves Internet bandwidth, server-client bandwidth, and local storage. It should be noted that in the case where the message is determined not to be spam, the interactions between MTA_0 and MTA_1 as shown in
The algorithm which implements the spam blocker is shown in
The algorithm begins in
If the reply is from MTA_1 it relays the reply to MTA_0 and waits for another reply.
If the reply is a HELO command as shown in
If the reply is a MAIL command as shown in
If the reply is a RCPT command as shown in
If the decision equation is determined to be true then the message is allowed and the time and to-address is entered in the allowed_connection database. The structure of the allow_connection database is shown in
If the decision equation is determined to be false then the message is not allowed and the time, from-address A_0, to-address A_1, and a reason for the rejection is entered into a rejected_connection database. The data structure of the rejected_connection database is shown in
If the reply is a DATA command as shown in
If the reply is a RSET, SEND, SOML, SAML, VRFY, NOOP, EXPN, HELP, or TURN command as shown in
If the reply is a QUIT command as shown in
If the reply is not a QUIT command then this is invalid command error and the algorithm sends a 500 to MTA_0 and waits for a new reply.
The algorithm for requesting the domain name server (DNS) pointer query in
The algorithm for the IP resolve test in
The algorithm for the open relay test in
The algorithm for the allow_address test in
The algorithm for the prevent_address test in
The algorithm for the echo_domain test in
The algorithm for the forged_domain test in
The algorithm for the bad_from address test in
The algorithm for the suspect_domain test in
The algorithm for the to_from test in
The algorithm for the no_filter test in
The algorithm for the yes_filter test in
The spam blocking process can be scaled to handle more messages by deploying more spam blocking units each connected to a client message transfer agent and changing the client's MX record to distribute the mail traffic among all the spam blocking units.
The spam blocking process can be made failsafe by deploying more spam blocking units each connected to a client message transfer agent and changing the client's MX record to distribute the mail traffic among all the spam blocking units and not to distribute mail traffic to any spam blocking unit which is off-line.
Objectives of this invention are to reduce the Internet bandwidth consumed by unsolicited messages, to reduce the communications bandwidth consumed between the client's message transfer agent and mail user agent, to reduce the amount of storage consumed by unsolicited messages, and to eliminate unsolicited messages from a client's e-mail box. This is accomplished by rejecting an unsolicited message before the body of the message is transferred to the client's message transfer agent.
Another objective of this invention is to improve the ability to detect unsolicited messages. This is accomplished by using the sending MTA's IP address, IP_0 which can not be forged. The problem is that content based tests suffer from the fact that the declared domain, from-address, subject line, or message body can easily be forged or changed. IP_0 can not be forged because a forged IP_0 would cause the receiving MTA's 220 rely to be sent to the wrong address and without a 220 reply the sending MTA would never be able to establish the requested connection. Source based tests are thus based on “bedrock” information while content based tests are based on “shifting sands.” This improves the ability of the spam blocker to detect suspected unsolicited messages.
Other objectives of this invention are to avoid the need for users to install software on their individual systems and the need to change the client's current message transfer agent. This is accomplished by positioning the spam blocker between the sending and receiving message transfer agents and not between the receiving message transfer agent and the mail user agent. This is further accomplished by not positioning the spam blocker as a message transfer agent add-on or mail user agent add-on. This is further accomplished by keeping the communications between the spam blocker and the sending and receiving message transfer agents standard SMTP protocol and eliminating other in-band or out-of-band communications channels between the spam blocker and the sending message transfer agent, receiving message transfer agent, or the mail user agent.
Another objective of this invention is to log the messages that have been allowed or rejected. This is accomplished by the allow_connection and the rejected_connection databases. This is further accomplished by deferring the decision equation until after the to-address A_1 has been transmitted and captured.
Another objective of this invention is to allow users to select the ability not to block unsolicited messages. This is accomplished by the no_filter test and the no_filter database. A related objective of this invention is to allow users to select the ability to block unsolicited messages. This is accomplished by the yes_filter test and the yes_filter database.
Another objective of this invention is to give feedback to the sender of a blocked message. This is accomplished by the sending a permanent negative completion reply such as a 550 reply to the sending message transfer agent if a message is determined to be unsolicited. The sending message transfer agent will then either send a error message to the sender or send the message back to the message transfer agent that sent the message. This is important since most spam blocking agents either delete or divert the spam into a junk folder and does not return an error message. The sender of a false positive unsolicited message would thus have no knowledge that the message was not delivered.
Other objectives of this invention are to scale the spam blocking process and to make the spam blocking process failsafe. This is accomplished by deploying more spam blocking units each connected to a client message transfer agent and changing the client's MX record to distribute the mail traffic among all the spam blocking units and not to distribute mail traffic to any spam blocking unit which is off-line.
The spam blocker algorithm shown in
Although the present invention has been described above in terms of specific embodiments, it is anticipated that alteration and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations and modifications as falling within the true spirit and scope of the invention.
Claims
1. A method for a receiving networked computer system with an Internet connection, a mail transport agent MTA_1, IP address IP_1, a domain name D_1, a recipient, A_1, an allow_address database, a prevent_address database, a suspect_domain database, a bad_from database, a no_filter database, a rejected_connection database, an allowed_connection database, and an operating system capable of executing the method to reject unsolicited messages from a transmitting networked computer system with an Internet connection, a message transfer agent MTA_0, an IP address of IP_0, a declared domain name D_0, a real domain name DD_0, and a sender address of A_0 comprising the steps of:
- a) waiting for a SMTP connection request on the receiving networked computer system's Internet connection;
- b) sending a 220 reply to MTA_0 to acknowledge the requested connection;
- c) extracting IP address IP_0 from the connection request;
- d) testing if the DNS database has a domain name DD_0 for IP_0;
- e) testing if IP_0 is in an open relay database;
- f) testing if IP_0 is in the allow_address database;
- g) testing if IP_0 is in the prevent_address database;
- h) requesting a connection with MTA_1;
- i) waiting for a 220 reply from MTA_1 to acknowledge the requested connection;
- j) waiting for a reply from either MTA_0 or MTA_1;
- k) jumping to step n) if the reply is not from MTA_1;
- l) relaying the reply from MTA_1 to MTA_0;
- m) jumping to step j) to wait for a new reply;
- n) jumping to step t) if the reply from MTA_0 is not a HELO;
- o) extracting domain D_0 from the reply;
- p) testing if declared domain D_0 of MTA_0 matches domain D_1 of MTA_1;
- q) testing if declared domain D_0 does not match real domain DD_0 of MTA_0 AND declared domain D_0 is in the suspect_domain database;
- r) relaying the HELO reply from MTA_0 to MTA_1;
- s) jumping to step j) to wait for a new reply;
- t) jumping to step z) if reply from MTA_0 is not a MAIL;
- u) extracting sender_address A_0;
- v) testing if A_0 is in the bad_from database;
- w) testing if DD_0 does not match the domain of A_0 and the domain of A_0 is in the suspect_domain database;
- x) relaying MAIL reply to MTA_1;
- y) jumping to step j) to wait for a new reply;
- z) jumping to step kk) if reply from MTA_0 is not a RCPT;
- aa) extracting recipient A_1;
- bb) testing if A_1 is in no_filter database;
- cc) testing if A_0 matches A_1;
- dd) jumping to step hh) if NOT(t_allow OR t_no_filter OR NOT (t_prevent OR t_open OR t_DD) OR t_bad_from OR t_suspect_domain OR t to_from OR t_echo_domain OR t_forged_domain);
- ee) logging time and recipient A_1 in the allowed_connection database;
- ff) relaying RCPT reply to MTA_1;
- gg) jumping to step j) to wait for a new reply;
- hh) logging the time, from-address sender_address A_0, recipient A_1, and the reason for rejecting the connection in the rejected_connection database;
- ii) rejecting the connection to MTA_0 by sending a 550 reply to MTA_0;
- jj) jumping to step j) to wait for a new reply;
- kk) jumping to step vv) if reply from MTA_0 is not DATA;
- ll) relaying DATA reply to MTA_1;
- mm) waiting for a 354 reply from MTA_1;
- nn) relaying the 354 reply from MTA_1 to MTA_0;
- oo) waiting for the data from MTA_0;
- pp) relaying the data from MTA_0 to MTA_1;
- qq) waiting for a.\r\n from MTA_0;
- rr) relaying the.\r\n from MTA_0 to MTA_1;
- ss) waiting for a 250 reply from MTA_1;
- tt) relaying the 250 reply to MTA_0;
- uu) jumping to step j) to wait for a new reply;
- vv) jumping to step yy) if reply from MTA_0 is not RSET, SEND, SOML, SAML, VRFY, NOOP, EXPN, HELP, or TURN;
- ww) relaying reply to MTA_1;
- xx) jumping to step j) to wait for a new reply;
- yy) jumping to step ddd) if reply from MTA_0 is not a QUIT;
- zz) relaying the QUIT reply to MTA_1;
- aaa) waiting for 221 reply from MTA_1;
- bbb) relaying 221 reply from MTA_1 to MTA_0;
- ccc) jumping to step a) to wait for a new connection;
- ddd) sending a 500 reply to MTA_0 to signal a syntax error; and
- eee) jumping to step a) to wait for a new connection, wherein t_allow represents the results of the testing in step (f); t_no_filter represents the results of the testing in step (bb); t_prevent represents the results of the testing in step (g); t_open represents the results of the testing in step (e); t_DD represents the results of the testing in step (d); t_bad_from represents the results of the testing in step (v); t_suspect_domain represents the results of the testing in step (w); t_echo_domain represents the results of the testing in step (p); t_to_from represents the results of the testing in step (cc); and t_forged_domain represents the results of the testing in step (q).
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Type: Grant
Filed: Jan 20, 2004
Date of Patent: Feb 10, 2009
Assignee: Engate Technology Corporation (Reno, NV)
Inventors: Richard Paul White (Pacific Grove, CA), Alan Huang (Menlo Park, CA), Haw-minn Lu (San Diego, CA), Ira Victor Spivack (Reno, NV)
Primary Examiner: Salad Abdullahi
Assistant Examiner: Anthony Mejia
Attorney: Imperium Patent Works, LLP
Application Number: 10/761,883
International Classification: G06F 15/16 (20060101);